Synchronous motor



22,1952 c. G. KRONMILLER ETAL ,583,

SYNCHRONOUS MOTOR Filed March 10, 1949 2 SHEETSSHEET l INVENTOR.

CARL G KRONM\\.LER BY mums H. G\LLE 1952 c. G. KRONMILLER ETAL 2,583,180

SYNCHRONOUS MOTOR Filed March 10, l949 2 SHEETS-SHEET 2 JNVENTOR. CARLG-KRONVNLLER \IJ\\.L\S H- GH-LE ATTORNEY Patented Jan. 22, 1952SYNCHRONOUS MOTOR Carl G. Kronmiller, Minneapolis, and Willis H.

Gllle, St. Paul, Minn., assignors to Minneapolis- Honeywell RegulatorCompany, Minncapolk, Minn, a corporation of Delaware Application March10, 1949, Serial No. 80,868

This invention relates to electric motors and more particularly to thesmall single phase synchronous type of low power electric motor suitablefor operating clocks or similar timin mechanisms. Small synchronousclock motors are generally old, particularly that type which utilizes asingle energizing winding for producing the magnetic field, and it is aprimary object of this invention to provide an improved motor of thisgeneral type which is simple in design, inexpensive to manufacture,which requires no maintenance and which utilizes a small amount of powerfor operation.

It is also an object of this invention to provide in a small synchronousmotor an improved design and arrangement of pole piece rings for thefield structure which carry the pole pieces, the rings being adapted forpunch press type of manufacture and which may be readily assembled intothe stator of the motor.

It is further an object of this invention to provide in a smallsynchronous motor an improved field structure which permits theutilization of a shading means which is common to all of the pole piecesenergized from a particular portion of the magnetic core of the motor.

It is still further an object of this invention to provide a. magneticfield structure in which there is radially an overlapping of the polepieces all oi which extend a maximum surface from which fiux linesemanate to the air gap to provide for improved flux distribution in thefield structure.

Another object of this invention is to provide in a small synchronousmotor of this type a field structure in which all poles originate fromone side of the energizing core and coil and extend axially of themotor, the poles being alternately shaded and unshaded and energizedfrom opposite ends of the magnetic core.

Another object of this invention is to providein a small synchronousmotor a field structure in which all poles originating from one side ofthe energizing core and coil and extending axially of the motor arealternately shaded and unshaded with the shaded and unshaded polesformed on separate pole rings.

Another object of this invention is to provide in a synchronous motorfield structure an arrangement of field poles extending axially of theaxis of the motor and separated into inner and outer groups spacedradially from one another to form an annular air gap therebetween intowhich a rotor is positioned, the individual poles of each group exposinga maximum portion of its surface to the rotor.

25 Claims. (Cl. 172-278) It is another object of this invention toprovide in a synchronous motor of this type an arrangement where theenergizing coil is separated from the pole portions of the magneticfield structure. rotor and gear train by an oil tight seal.

A further object of this invention is to provide a. motor in which theenergizing coil may be removed from the field structure withoutdisassembling any other portion of the motor.

It is also an object of this invention to provide in a synchronous motoran arrangement in which the rotor is mounted on and journaled in a geartrain which is mechanically independent of the magnetic field structure.

Another object of this invention is to provide in a synchronous motor anoil tight cavity in which the gear train, rotor. and field portions arelocated remote from the energizing coil of the motor, and into whichcavity access can be had for oiling purposes without removing orpuncturing the enclosing elements.

These and other objects of this invention will become apparent from areading of the specification together with the drawing in which,

Figure 1 is a sectional view of one embodiment of the motor showing thelocation and arrangement of the field structure parts, and

Figure 2 is a top view of the motor of Figure l with the rotor and geartrain removed to show the positioning of the pole pieces in the fieldstructure.

Figure 3 is a top view of the preferred embodiment of this motor designwith the cover removed and the gear train shown in phantom to give adisclosure of the positioning of the field structure parts.

Figure 4 is a side elevation view of the motor of Figure 3 with thefield structure shown in section taken along the line 4-4 in Figure 3,the gear train shown in full, and the rotor and cover shown in sectionto disclose the relationship of the motor parts.

Figure 5 is a top-view of the preferred embodiment of the motorcompletely assembled.

The embodiment of the small synchronous clock motor disclosed in Figuresland 2 comprises essentially a magnetic field structure or statorindicated generally at I! and a rotating element or rotor indicated atH. The improvement in the motor design lies in the design andarrangement of the parts of the magnetic field structure I! and it is tobe understood that this element may be used with any of the conventionaltypes of rotating elements to give a synchronous motor design, aninduction motor design. or a hysteresis or eddy current type of motor.Referring to the drawings in detail, it will be seen that the magneticfield structure l2 includes a cup-shaped structure which houses theparts of the field structure and rotor and which also performs afunction in the motor design which will be later indicated. Thecup-shaped structure has been disclosed in the drawing as containing twoparts; a cylinder I3 and an end plate I4, both of magnetic material, butit is to be understood that these two parts can be integral with oneanother. Cylinder i3 is flared or enlarged throughout one portion toprovide a shoulder l5 at which a sealing plate ii of nonmagneticmaterial is located. Sealing plate I. is secured to the cylinder l3 bysilver solder or any other suitable sealing material. The center of thisplate has an aperture therein through which is positioned a cylindricalcore of magnetic material 11. Sealing plate 16 fits over a reducedportion 25 of core I! and is similarly sealed to the core at thissurface with a silver solder. Magnetic core I1 and the sealing plate l5divides the cylinder l3 into two chambers, one'of which contains theenergizing winding 2| of the motor which is positioned on or about themagnetic core. End plate I4 of the cup-shaped magnetic structureencloses this portion of the cylinder which contains winding 2| and issecured to the magnetic core by suitable means such as'a screw 22.Should the cup-shaped structure be a single piece, the

method of fabricating or assembling the motor would be somewhat changedin that the winding would be inserted on the magnetic core and thesealing plate added to enclose the winding. With this arrangement thewinding could not be removed or checked without removal of the sealingplate.

Positioned above the sealing plate is that portion of magnetic fieldstructure I2 which carries the pole pieces. This portion of the magneticfield structure is composed of a plurality of pole piece rings 23, 24,25, and 26 of which the outer rings 23, 24 are common to the cylinder l3and hence through plate M to one end of the magnetic core l'I while theinner rings 25, 26 are common to the opposite end of the magnetic coreI] or the reduced portion 20 of said member. Each of the rings 23, 24,25 and 25 is annular in shape and contains four pole teeth 0! Polepieces equally spaced apart, as will be later identified, which is bentor extend normal to the plane of said rings. Thus the outer pole ring 23contains pole pieces 33 on the inner periphery of the ring whichextendnormal to the plane of the ring. Similarly the, pole piece ring 24contains four pole pieces 34 which are located onthe inner periphery ofthe ring and extend normal to the plane of the ring. The inner polepiece rings 25, 26 each contain four poles or pole pieces 35, 36respectively which are located on the outer periphery of said rings andextend normal to the plane of said rings. Quter pole rings 23, 24 are sopositioned that the pole pieces 33, 34 respectively thereon extend in adirection of one another and the rings 23, 24 are separated by shadingmeans 31 which herein is an annular ring of copper. Two such rings aredisclosed in the present structure and these rings assist in spacing thepole piece rings a given distance apart such that the extent of the polepieces 33, 34 cover substantially the distance between the rings. Rings23, 24 may be held in position by any means such as a silver solderconnection (not shown) at the upper surface of pole piece ring 24 whereit abuts the wall of the cylinder l3. The inner pole piece rings 25, 28are similarly positioned such that the pole pieces thereon 35, 33respectively extend toward one another or in the direction of theopposite ring, and these rings are spaced apart by shading means 38which take the form of circular or annular copper rings.

Here also, two such rings are used to provide proper shading andspacing. The inner pole piece rings 25, are secured to the core memberll by means of a clamping nut 40 which is screwed onto a threadedsection of the upper portion 20 of the magnetic core II. It will benoted that the spacing of the inner and outer pole rings provides anannular air gap 4| in which the rotor assembly H is positioned.

The rotor assembly H is comprised of a cupshaped frame 42 of anonmagnetic but electrically conductive material, such as aluminum. anda band of magnetic material 43 having a high hysteresis coefficient.Band 43 is positioned on the wall portion of the cup-shaped frame 42such that it extends between the pole pieces of the magnetic fieldstructure. The cup-shaped frame 42 is secured to a shaft 45 by means ofbushings 45 pressfitted onto a" shaft 45 on either side of the frame 42.The shaft 45 fits into a sleeve 45 of bearing material which is locatedin an aperture 48 in the magnetic core", which sleeve provides bearingsurfaces for the shaft. The upper portion 20 of magnetic core I'l'alsoincludes an aperture in which is positioned a wick 41 containing oil forlubricating the bearing connection between the shaft 45 and the sleeve43. The opposite end of the shaft 45 is journaled in a gear assemblyindicated at 50 (shown in full in Figure l) which assembly is alsohoused in the upper portion of the cylinder II. The gear assemblyincludes two brass side plates 5! secured in a spaced relationship bybushings 52 and housing a plurality of gears and pinions 53 whichcooperate with the shaft 45 and the output shaft and pinion 55. Thespeed of the present motors, as will be discussed later, is 900 r. p. m.on a 60 cycle input since it is an eight pole synchronous motor and thegearing arrangement used herein reduces the output speed at the pinion55 to 8 r. p. m. The gear assembly 50 may be secured in any manner (notshown) to the cylinder l3.

In the magnetic field structure 12 heretofore described it is the shapeand the arrangement of parts which represents the advance in the smallsynchronous motor art. Pole pieces 33 and 34 of the outer pole piecerings extend axially of the motor axis and are arranged in pairs suchthat each pair subtends a greater angular distance or is wider than thespace between the consecutive pairs of pole pieces. In this structurefour such pairs appear. Of the individual pole pieces 34 and 33 of therespective rings the pole pieces 34 subtcnd a larger angle or are andare of greater width than the pole pieces 33. The upper pole piece ring24 and hence the pole pieces 34 of that ring are the shaded poles of theouter pair of pole rings 23, 24 and hence the shaded poles are largerthan the unshaded poles in this arrangement. The axial disposition ofthe pole pieces 33, 34 represents a large pole face area to the rotor llthus utilizing a maximum of fiux lines present in these members toeffect a maximum efilciency of the motor. Similarly the structure of theinner pole piece rings 25, 25 includes four unshaded poles 35 and fourshaded poles 35 extending axially of the motor and presenting largeshaded poles 35 which similarly subtend a larger angle than the unshadedpoles 35. The shaded pole ring 25 for this arrangement is 10- aseaieo scated above or on top 01' the lower pole piece ring 24. In thisarrangement also the individual rings are so positioned that there areformed pairs of pole pieces each pair including a shaded and an unshadedpole with a greater angular distance being occupied by the pairs of polepieces than by the space between each consecutive or adjacent pair ofpoles. As heretofore noted the arrangement herein represents an eightpole synchronous motor. The space occupied by the pairs oi poles angularis the same for the outer and inner pole piece rings but because of thediflerence in radii from the center of the masnetic core to therespective rings, the inner pole piece rings will subtend a shorterlinear distance along an are drawn from the center of this motor thanwill each pair on the outer pole of pole rings. Angularly, each pair ofpole pieces subtends an arc distance which is slightly greater than 22degrees and the space between each pair of such poles is slightly lessthan the arc of 22 degrees. This arrangement gives an overlappingbetween the consecutive or adjacent pairs of pole pieces on the innerand outer pole piece rings 23, 24, 25, 28 respectively. The rings are sopositioned also that the shaded pole for each ring overlaps an unshadedpole on the opposite ring in the adjacent pairs of pole pieces. Thisoverlapping gives a desired bridging eflect between the pole pieceswhich provides for a better distribution oi the magnetic fiux lin in themagnetic field structure. With the arrangement shown in Figure 2, therotation of the magnetic field and hence the rotor will be clockwise asviewed from the top of the motor.

In operation, this motor is generally similar to a synchronous motor.The energizing winding II on the magnetic core i1 is energized from asingle phase source (not shown). Upon energization the magnetic core I!is polarized or magnetized such that a different polarity exists ateither end of the magnetic core. This polarity changes with the changein the direction of current fiow from the energized source. The end ofthe magnetic core ll abutting the end plate l4 energizes the outer polepiece rings 23, 24 through the magnetic path of the end plate I4 andwalls of the cylinder is. Thus the outer pole piece rings each receiveflux lines from this end of the magnetic core. Similarly the inner polepiece rings 25, 26 receive its energizing fiux from the upper end of themagnetic core II or the end to which they are common. The inner andouter pole piece rings will then be energized magnetically with flux atan opposite polarity. The magnetic circuits for the flux lines from thecore II includes the end plate I 4, cylinder l3, rings 23, i4 andassociated pole pieces 33, 34, rotor ll, rings 25, 26 and associatedpole pieces 35, 36 and magnetic core il. Depending upon instantaneouspolarities due to the alternating energizing current, the fiux willtraverse the magnetic circuits in one direction or the other movingacross the air gap Ill and through the rotor ll, between pole pieceswhich are energized at that instant. The shading rings 31 and 38 betweenthe outer and inner rings respectively are so located that they affectthe fiux lines entering, in each case, the upper pole piece ring 24 or25 respectively. The flux lines in these upper inner and outer ringspass through circuits which include the shading rings 31, 38 and areretarded by the efiect of the short-circuited electrical conductor in amanner well known in the art. With the arrangement and spacing of therespective shaded and unshaded pole pieces in each pair and between thepairs, it will be seen that a rotating fiux field is obtained which actsupon the rotor assembly i I in a well known manner. The aluminumcup-shaped frame 42 acts as an induction motor to provide sufiicientstarting torque and as synchronous speed is approached, the hard steelrotor band 43 of this rotor assembly becomes polarized or permanentlymagnetized with poles such that the motor locks in a synchronous speedof 900 revolutions per minute.

The preferred embodiment of our motor design which is disclosed inFigures 3. 4 and 5 contains substantially the same magnetic fieldstructure or stator arrangement disclosed in Figures 1 and 2 butincludes certain improvements which will be pointed out below. Thispreferred motor contains generally three main components: namely, themotor field assembly indicated generally at 60, the gear train and rotorassembly indicated at BI and the cover assembly indicated at 62.

The motor field assembly has a centrally located magnetic core 63 uponwhich is positioned an energizing winding 64. Associated with themagnetic core 53 and winding 64 is the magnetic field structure composedoi pole piece rings and shading means later to be identified. Oneextremity of said magnetic core 63 has a tapped aperture 66 into whichis threaded a screw 66 to secure an end plate 61 to said end of themagnetic core. gizing winding 64 and abutting against the end plate 81is an outer pole piece ring 10 of the magnetic field structure for motorfield assembly 60. Outer pole piece ring III is generally cylindrical inform having an upper section of reduced diametrical dimensions II, atransverse ring-like section 12 normal to the cylindrical portion of thering and four downwardly extending pole pieces 80 which originate fromthe transverse section of the pole piece ring 10, as seen in Figure 4. Ashoulder 13 is formed between the main portion of the ring 10 and thereduced diametrical section 'II for purposes which will be later noted.From a comparison of Figures l and 2 with the preferred embodiment ofthis invention it is to be seen that the outer pole piece ring III isactually a composite structure including a portion of the cylindricalcasing iii of Figure l and the upper pole piece ring 24 of Figure 1,thereby providing the housing for the core BI and coil 84 of the motor.It will be readily understood that the end plate 61 and pole piece ring10 are made of a magnetic material and thereby a magnetic path from oneextremity of the magnetic core 63 to the outer pole piece rings isprovided.--

The extremity of the magnetic core 63 opposite the tapped aperture has aportion or section 14 of reduced diametrical dimension and an aperture15 centrally located with the axis of the magnetic core. An annulardisk-like sealing plate It is fitted down over the reduced portion 14 ofmagnetic core 63 to abut at its inner periphery against the shoulderformed by the reduced portion I4 and the main portion of the magneticcore 63. Annular sealing plate 16 also abuts against the outer polepiece ring I0 at the shoulder 13 formed between the reduced diametricalsection II and the outer portion of the pole ring 10. The annularsealing ring is sealed by any suitable method (not shown) to the annularpole piece ring 10 and the magnetic core 63 to provide an oil type sealat these two areas of abutment. As in the embodiment of Surrounding core63 and ener- Figures 1 and 2, sealing plates 18 partitions theenergizing winding 84 from the remaining portion of the motorto providean oil type cavity within which the energizing winding is located.

Located directly 'above the sealing plate 18 are the pole piece ringsand pole pieces of the magnetic field structure. As previously recitedthe outer pole piece ring 18 included a ring-like portion 12 from whichthe pole piece 88 originated. A cooperating outer pole piece ring 8|having pole pieces 82 originating therefrom is positioned in abuttingrelationship with this seal plate 16 and abutting against the reducedportion H of the outer pole piece ring 18. The pole pieces 88 and 82 ofthe outer pole piece rings 18 and 8| are positioned axially of themagnetic core, as in the embodiment of Figures 1 and 2, and havepositioned therebetween ring-like shading means 84. As in the firstdescribed embodiment, the pole piece rings are so positioned that thepole pieces thereon extend in the direction of one another to enclosethe shading means 84. Outer pole piece rings 18 and 8|, shading means 84and the ring-like seal plate 18 are held in, assembled relationship bythree rivet-like members 88. The rivet-like members 85 are irregular inshape having a main body portion of one dimension which fits downthrough apertures in the pole piece rings "and 8|, shading means 84 andseal plate 16 to be riveted over or flatted out against the under sideof the seal plate. Rivet members 85 also have a shoulder portion 88which keeps the main body of the rivet from passing through theapertures in the shading means, pole piece rings and seal plate; andabove this portion another section of reduced diameter, the purpose ofwhich will be later described. This upper portion of the rivet member 88and the shoulder portion 88 have a tapped aperture therein which as willbe later described provide the means for mounting for the gear trainassembly 8|.

The portion of the magnetic field 68 heretofore described is assembledby placing in the outer pole piecering 18, the shading means 84, polepiece ring 8| and the seal plate 15 and securing the same in assembledrelationship by means of rivets 88. Magnetic core 83 is then insertedthrough the aperture in seal plate 16 to the extent of its reducedportion 14 and as will hereinafter be described, inner pole piece rings88, 8| are assembled on this reduced portion and secured thereto. Plate18, as heretofore described is then sealed to pole piece ring 18 andcore 88 to provide the oil tight cavity for winding 84. End plate 81 issecured to core 83 to enclose the winding or energizing coil.

The reduced section I4 of magnetic core 63 against which the innerperiphery of the seal plate 18 abuts serves as the mounting area for thepair of inner pole piece rings 88 and 8|. These inner rings abut attheir inner periphery against the reduced section 14 of magnetic core 88and have emanating from their outer periphery the pole pieces 82, 83respectively in the same manner as that described in Figures 1 and 2.The pole pieces 82, 83 are bent normal to the general plane of the polepiece rings and when positioned on the magnetic core extend axially ofthe magnetic core. Positioned between the pole piece rings 88 and 8| isthe inner shading means 84, the pole piece rings being so positionedthat the pole pieces thereon extend in the direction of one another toenclose the shading means 84. The inner pole pieces 82, 83 of pole piecerings 88, II respectively are positioned at a shorter radial distancefrom the geometric center of the motor or axis of the magnetic core thanthe pole pieces 88, 82 of the outer pole piece rings 18, 8| to providetherebetween an annular air gap such as can be seen in Figure 3 and hasbeen previously described in Figures 1 and 2. These annular pole piecerings are secured on the reduced section 14 of the magnetic core 83 bymeans of an operation which entails bending over the upper extremity ofthe magnetic core 83 as canbe seen in Figure 4. Such an operation isaccomplished by placing a suitably conically shaped tool in the aperture18 of the magnetic core 88 and bending or pressing the upper extremityof the reduced portion I4 into an overlapping relationship with theupper pole piece ring 8|.

The structure thus far described constitutes the motor field assembly 88and the preferred embodiment of our invention. With the exception of theshading means 84 and 84, the seal plate I8 and the winding 84, allportions of this structure are made of a magnetic material. The shadingmeans 84, 84 are constructed from an electrically conductive material ina well known manner and a seal plate 18 is made of a nonmagneticmaterial. As was described in connection with Figures 1 and 2, the polepiece rings 18, 8|, 88 and 8| are so positioned that the pole piecesthereon form pairs of shaded and unshaded pole members with a greaterangular spacing between the consecutive pairs for the inner and outerstructures than is found between the pole pieces of each consecutivepair. Similarly, as in Figure 1, the consecutive pairs of pole pieces onthe inner and outer rings are so positioned that the pairs on onesection are positioned adjacent the space between the adjacent pairs onthe opposite or outer section. The magnetic field structure of the motorfield assembly 88 produces a rotating flux ileld from single phaseenergization of the winding 84 in the same manner as that described inconnection with Figures 1 and 2 and hence will not be further describedhere. Field coil 84 on magnetic core 83 is energized through electricalconductors I88 which pass through suitable apertures (not shown) in themain portion of outer pole piece ring 18 to be connected to theextremities of the winding 84.

Motor field assembly 88 is designed to mount and position the gear trainand rotor assembly 8| through connections to the rivet members 88,heretofore described, which hold the outer pole piece rings 18, 8| inassembled relationship. .The mechanical connection between the geartrain and rotor assembl 8| and the motor field assembly 68 is madethrough nonmagnetic parts and the rotor of the former assembly, which isits only component made oi magnetic material, is the only part inmagnetic association with the motor field assembly.

Referring now to Figure 4, it will be seen that the gear train and rotorassembly is shown in full with the exception of the rotor which is shownin cross section. It will further be seen that the motor field assemblyis shown in cross section such that a disclosure of the association ofrelationship of parts can be had. Similarly the cover assembly 82 isshown in cross section to disclose the gear train and the sectionalportion of the motor field assembly. The rotor of this motor includes acup-shaped member I83 of nonmagnetic but electrically conductive mate'-rial. This cup-shaped member I83 is a machined part having a centrallylocated hub pormotors.

tion I04 which .fits into the aperture I! of the magnetic core 63 andmounts the shaft I05 of the rotor. The cup-shaped portion of the rotorhouses a hardened steel band I of high magnetic retentivity on the innerwalls of the upstanding portion of this cup-shaped member. The band I06is press fitted into the cup-shaped member and held there due to thefrictional force of engagement between the members. Band I is notchedabout its lower periphery, as can be seen at I01 in Figure 4, thenotches assisting in defining the polar regions of a magnetic rotor asthe rotating element reaches a synchronous speed. This rotor issubstantially that described in connection with Figures 1 and 2 and isgenerally well known in the art of small synchronous As previouslyindicated, the rotor is p0- sitioned between the pole pieces on theinner and outer pole piece rings in an air gap obtained by the spacingsof these elements and is designed to rotate within that air gap aboutthe axis of shaft I05.

This rotating element or rotor is journaled in the remaining portion ofthe gear train and rotor assembly 0| within suitable bearing elements,as will be later described. contained in the side plates IIO of the geartrain and rotor assembly. The side plates IIO which house and Journal aplurality of gears and pinions III are held in spaced relationship byspacer members H2 and I I3, these members having shoulder portions I09at their extremities. 'Spacer members H2 and II 3 fit through aperturesin the side plates I0u and have portions riveted over on the innersurface of the lower gear plate, as at H4, and at the outer surface ofthe upper gear plate (not shown) to maintain a rigid and assembledrelationship of these elements. Spacer members H2 and II: have centralapertures through which mounting screws II5 extend into contact with therivet members 05 to engage the latter in a threaded relationship securingear train to the motor field assembly. The spacer members H2 and I I Jof the gear train are three in number and are identical with theexception that the spacer II3, one of which appears in the gear train,has a transverse duct H6 or aperture located approximately midwaybetween the side plates IIO. Duct II6 extends to or connects with themain axial aperture of spacer element H3. The purpose of this duct IIGwill become evident as the disclosure proceeds.

On the underside of the lower side plate IIO, as seen in Figure 4, thereis positioned a felt pad III having the general configuration of theside plate, and this pad is held in position by a retaining plate I20.Shoulder portions on the spacer elements H2 and H3, as previouslydescribed. hold the retaining plate and the pad in abutting relationshipwith the side plate IIO. Retainer plate I and felt pad II! haveapertures therein through which a bearing member I2I which is mounted onthe lower plate 0 extends, this latter member journaling the shaft I05of the rotor. Upper plate III! also journals shaft I05, but becausemember I2I takes most of the load of the rotor, no specific bearingmember need be provided therein. Bearing member I2I may be of anysuitable bearing material.

The shaft I05 as noted above is journaled in bearing member I2I and anaperture in upper side plate H0. A pinion I22 mounted on the shaft I05between the side plates cooperates with the plurality of pinion andgears III of the gear train to drive the latter and position an outputshaft or pinion I23 of the gear train in a well known manner. The outputshaft and pinion I23 of the gear train are similarl journaled in abushing member or bearing member I24 and the lower side plate I III. Theextremity of bushing I24 outside the confines of the side plates III! isthreaded, as at I25, for purposes which will be later noted. Positionedon the upper side of the upper side plate Iluis a second felt pad I30.which as will be later noted is held in position by the cover assembly62.

Cover assembly or includes a cover I32 and the lock nut l3i. cover I32is cup-shaped in form and is of the same diametrical dimension as themain portion of the motor held structure such that it may at down overthe reduced portion II of outer pole piece ring I0 to provide a motorwhich is cylindrical in roi'm. The upper portion of the cover isrecessed as at I33, as shown in Figure 5. Within tn... recess is anaperture through which the tapped section I25 of the bearing sleeve I24extends to be engaged by the lock nut I3l. Lock nut I3I is threaded ontothe threaded portion I25 to secure the cover I32 in place on the motorfield assembly and gear train assembly. It will be noted in Figure 4that the screws H5 which lit down into the two spacer elements 2 andsecure the same to toe motor field through the rivet members arepositioned underneath the cover. Appropriate raised portions in thegeneral configuration of the recess I33, as shown in Figure 5 provideclearance for the heads of the screws so that the cover can be fitteddown in closely assembled relationship with the gear train. The screw ,5which passes through the spacer member II3, however, is not positionedunderneath the cover, but rather, as indicated in Figure 5, extendsthrough an aperture in the cover, and passes through the spacer member II0 and into the tapped portion of the rivet member t5 to secure thisportion of the gear train and also the cover in assembled relationship.As was previously noted spacer element I I3 has a transverse duct llb'connected to the centraLaperture in the spacer member. The screw whichfits into this spacer element is adapted to be removed from itsassembled position without removing the cover. When this screw isremoved a passageway is provided from outside the cover to the interiorof the gear train such that the motor may be reoiled withoutdisassembling the motor. The cover assembly is made oil tight with theremaining portion of the motor by means of a rubber basket I3Ipositioned between a portion of the sleeve I24 and the cover I32.Similarly the screw IIB which passes through sleeve II3 from without thecover, as well as the circular surface of the cover as it engagesthepole piece ring 10 are sealed with a suitable sealing material notshown. Thus, when the motor is completely assembled a sufficientquantity of oil may be applied to the felt pads, and the motor so sealedas described above as to prevent escape of the oil from the exterior ofthe motor. It will be further noted that the seal plate 10 prohibits theoil from entering the recess or cavity wherein the energizing coil islocated and hence no oil will be lost through absorption by this member.

The motor described in the preferred embodiment operates in the samemanner as that described in connection with the Figures 1 and 2. Thepole piece rings I0, 8|, and SI with their associated pole piecesreceive the flux lines emanating from the respective ends of themagnetic core and provide a rotating flux field as heretofore described.In the present arrangement the pole pieces 80 of outer ring '10 and thepole pieces 93 of inner ring ii are shaded by the respective shadingmeans 84 and 94. The pole pieces cooperate with the rotor members I03and 108, that is, the electrically conductive element and the magneticelement, to provide a self starting synchronous motor of the hysteresistype. This motor as described in connection with Figures 1 and 2 is an8-pole synchronous motor having a synchronous speed of 900 R. P. M. with60 cycles energization. The gear train disclosed in the drawings and notdescribed in detail includes the gear and pinion members to effect areduction in speed from 900 R. P. M. to 8 R. P. M.

The magnetic field structure described in connection with theembodiments of our invention is one which is easily manufactured andalso easily assembled to provide a compact highly efficient unit formotors of this type. The present motor designs described herein operateon less than 2 watts power input and have an exceptionally low pull-inand drop-out voltage requirement with a high pull-in torque and a lowdropout torque. They further provide sufficient overall power output tomeet the demands on such small motors. with the present motor designs itis possible to maintain the energizing windings separate from the polepiece rings andgear train and thus keep this'portion entirely free ofoil or immersed in a suitable cooling medium if desired.

The embodiment of Fi res 3, 4 and 5 further discloses a preferredarrangement of gear train, rotor and cover such that an oil tight unitis provided capable of giving exceptionally long life performance.Should it become necessary to add additional lubricant to the gear trainafter the motor has been in use for some time, the same can beaccomplished by simply removing the exposed cover screw and insertingthe oil through passage heretofore described. This operation does notentail disassembling the motor or disturbing the remaining oil seals inany manner. After the motor has been oiled the screw is'again insertedand covered with a suitable material in such a manner that the originaloil tight motor design is again obtained.

In considering this invention it should be kept in mind that the presentdisclosure is intended to be for a large part illustrative only and thescope of the invention is to be determined only by the appended claims.

Weclaim:

1. In a motor. a magnetic field structure including an energizing corewith a winding thereon and a plurality of pole piece members attached tosaid magnetic core, one of said pole piece members being cup shaped inform and positioned to artially enclose said core and winding, said oneof said pole piece members having a peripheral shoulder thereoncontinuous in form, a rotor magnetically associated with said fieldstructure.

on said field structure. and easing means having a periphery of the sameshape as said shoulder resting on said shoulder of said pole piecemember and enclosing saidgear train and rotor.

2. In a motor, a magnetic core with an energizing winding thereon. amagnetic field structure energized by said magnetic core and includingpole piece structures attached to either end of said magnetic core, oneof said pole piece structures having a shoulder thereon. each of saidpole piece structures having pole pieces thereon originating from saidpole piece structures at the same radial region with respect to one endof -a gear train connected to said rotor and mounted 12 said magneticcore and extending axially of said magnetic core, shading meansencircling alternate pole pieces of each of said pole piece struc--tures to provide alternately shaded and unshaded pole pieces, a rotormagnetically associated with said field structure, a gear train attachedto said rotor and mounted on said field structure, and a cover memberresting on said shoulder of one of said pole piece structures andenclosing said gear train.

3. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure energized by said magnetic core andincluding a plurality of inner and outer pole piece rings, said innerand outer pole piece rings each having pole pieces thereon which arepositioned axially of said magnetic core and which ole pieces extendtoward the opposite pole piece ring, shading means located between saidrings to provide rings of shaded and rings of unshaded pole pieces, saidouter and inner rings being so positioned that the pole pieces thereonform pairs of shaded and unshaded pole pieces with a greater spacingbetween the pairs than between the pole pieces of each pair, a path ofmagnetic material connecting one end of said magnetic core to said outerpole piece rings, means securing said inner pole piece rings to theopposite end of said magnetic core, and a rotor magnetically associatedwith said magnetic field structure.

4. In a synchronous motor, a magnetic core with an energizing windingmounted thereon, a magnetic field structure nergized from said magneticcore and including a plurality of inner and outer pole piece rings, saidinner and outer pole piece rings each having pole pieces thereon whichare positioned axially of said magnetic core and which pole piecesextend toward the other of said inner or outer pole piece rings, shadingmeans positionedbetween said inner and outer pole .piece ringsrespectively to provide rings of shaded and rings of unshaded polepieces, said outer and inner rings 'being so positioned that the polepieces thereon form pairs of shaded and unshaded poles with a greaterspacing between said pairs of pole pieces than between the pole piecesof each pair, a path of magnetic material connecting one end of saidmagnetic core to said outer pole piece rings, means connecting saidinner pole piece rings to the other end of said magnetic core, saidinner and outer pole piece rings being disposed from one another to forman annular air gap therebetween, and a rotor positioned within saidannular air gap.

5. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure energized from said magnetic coreand including a plurality of inner and outer pole piece rings, saidinner and outer pole piece rings each having pole pieces thereon whichare positioned axially of said magnetic core and which pole piecesextend toward the other of said inner and outer pole piece rings,shading means positioned between said rings to provide rings of shadedand rings of unshaded poles pieces, said outer and inner rings being sopositioned that the pole pieces thereon form pairs of shaded andunshaded poleswith a greater spacing between the pairs and between thepole pieces of each pair, means connecting said inner and outer. polepiece rings to opposite ends of said magnetic core, the pairs of polespieces on said inner ring being so located that the radial lines drawnthrough the middle of each inner pole piece passes through the spacingbetween the pairs of said outer pole pieces, said inner and outer polepiece rings being so positioned relative to one another to provide anannular air gap therebetween, and a rotor positioned within said annularair gap.

' 6. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure energized from said magnetic coreand including a plurality of inner and outer pole piece rings, saidinner andouter pole piece rings each having pole pieces thereon whichare positioned axially of said magnetic core and which pole piecesextend toward the other 01' said inner and outer pole piece rings,shading means positioned between said rings to provide rings of shadedand rings oi unshaded pole pieces, said outer and inner rings being sopositioned that the pole pieces thereon form pairs of shaded andunshaded poles with a greater spacing between the pairs than between thepole pieces of each pair, means connecting said inner and outer polepiece rings to opposite ends 01' said magnetic core, the outer edges ofeach pair of inner pole pieces overlapping an outer edge of one polepiece in adjacent pairs of outer pole pieces, said inner and outer polepiece rings being so positioned relative to one another to provide anannular air gap therebetween, and a rotor positioned within said annularair gap.

7. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure energized from said magnetic coreand including a plurality oi inner and outer pole piece rings, saidinner and outer pole piece rings each having pole pieces thereon whichare positioned axially of said magnetic core and which pole piecesextend toward the other of said inner and outer pole piece rings,shading means positioned between said rings to provide rings of shadedand rings of unshaded pole pieces, said outer and inner rings being sopositioned that the pole pieces thereon form pairs or shaded andunshaded poles with a greater spacing between the pairs than between thepole pieces of each pair, means connecting said inner and outer polepiece rings to opposite ends oi said magnetic core, the shaded polepieces of said inner and outer pole piece rings having a larger crosssectional area than the unshaded pole pieces of said rings, said innerand outer pole piece rings being so positioned relative to one anotherto provide an annular air gap therebetween, and a rotor positionedwithin said annular air gap.

8. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure energized from said magnetic coreand including a plurality oi inner and outer pole piece rings, saidinner and outer pole piece rings each having pole pieces thereon whichare positioned axially of said magnetic core and which pole piecesextend toward the other of said inner and outer pole piece rings,shading means positioned between said rings to provide rings of shadedand rings of unshaded pole pieces, said outer and inner rings being sopositioned that the pole pieces thereon form pairs of shaded andunshaded poles with a greater spacing between the pairs of and betweenthe pole pieces of each pair, means connecting said inner and outer polepiece rings to opposite ends or said magnetic core, the shaded poles ofeach pair of pole pieces on said inner and outer pole piece ringsoverlapping the unshaded pole pieces of each adjacent pair of polepieces on the other ring, said inner and outer pole piece rings being sopoannular air gap therebetween, and a rotor positioned within saidannular air gap.

9. In a synchronous motor. a magnetic core with an energizing windingthereon, a magnetic field structure energized from said magnetic coreand including a plurality of inner and outer pole piece rings, saidinner and outer pole piece rings each having pole pieces thereon whichare positioned axially of said magnetic coreand which pole pieces extendtoward the pole pieces of the other inner or outer pole piece ring,shading means located between said rings to provide rings of shaded andrings of unshaded pole pieces, said inner and outer pole piece ringsbeing so p0- sitioned that the pole pieces thereon i'orm pairs oi shadedand unshaded poles at a greater spacing between said pairs than betweenthe pole pieces of each pair, means connecting said inner and outer polepiece rings to opposite ends oi said magnetic core, the shaded poles oneach pair of pole pieces on said inner and outer pole piece ringsoverlapping the unshaded pole pieces of the adjacent pairs on saidrings, and a rotor of magnetic material magnetically associated withsaid magnetic field structure.

10. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure energized from said magnetic coreand including a plurality oi inner and outer pole piece rings, saidinner and outer pole piece rings each having pole pieces thereon whichare positioned axially of said magnetic core and which pole piecesextend toward the pole pieces of the other inner and outer pole piecerings, shading means positioned between said inner and outer pole piecerings to provide rings of shaded and rings of unshaded pole pieces, saidinner and outer pole piece rings being so positioned that the polepieces thereon form pairs of shaded and unshaded poles with a greaterspacing between said pairs than between the pole pieces 01' each pair,means connecting said inner and outer pole piece rings to opposite endsof said magnetic core, said shaded pole pieces of said inner and outerpole piece rings having a larger cross sectional area than the unshadedpole pieces of said rings, and a rotor of a magnetic materialmagnetically associated with said magnetic field structure.

11. In a synchronous motor, a magnetic core. a magnetic field structureadapted to be energized from said magnetic core and including aplurality of inner and outer pole piece rings, said inner and outer polepiece rings each having pole pieces thereon which are positioned axiallyof said magnetic core and which pole pieces extend toward the polepieces of the other of said inner and outer pole piece rings, shadingmeans positioned between said rings to provide rings of shaded and ringsof unshaded pole pieces, said inner and outer pole piece rings being sopositioned that the pole pieces thereon i'orm pairs of shaded andunshaded poles with a greater spacing between said pairs than betweenthe pole pieces of each pair, means connecting said inner and outer polepiece rings to opposite enfs of said magnetic core, said inner and outerrole piece rings being so positioned relative to one another to providean annular air gap therebetween, said shaded pole pieces of said innerand outer pole piece rings subtending a greater angular distance thansaid unshaded pole pieces of said rings, and a rotor of magneticmaterial positioned in said annular air gap.

12; In a synchronous motor. a magnetic core with an energizing windingthereon, a magnetic field structure energized by said magnetic core andincluding a plurality oi inner and cuter pole piece rings, said innerand outer pole piece rings each having pole pieces thereon which arepositioned axially of said magnetic core, shading means located betweensaid rings to provide said rings of shaded and rings of unshaded polepieces, said' outer and inner rings being so positioned that the polepieces thereon i'orm pairs of shaded and unshaded pole pieces with agreater spacing between the pairs than between the pole pieces of eachpair, a path of magnetic material connecting one end of said magneticcore to said outer pole piece rings, means securing said inner polepiece rings to the opposite end or said magnetic core, and a rotormognetically associated with said magnetic field structure.

13. In an alternating current motor, a magnetic core with an energizingwinding thereon, a magnetic field structure energized by said magneticcore and including pole piece structures attached to either end oi! saidmagnetic core and being concentric thereon, each oi. said pole piecestructures including a pair of pole piece rings having pole piecesthereon extending axially of said magnetic core, all of said pole piecesoriginating from said pole piece structures at the same radial regionwith respect to one end of said magnetic core, an annular portionincluded in one of said pole piece structures and exclusive of said polepieces thereon which partially encloses said magnetic core, and saidwinding thereon, a single' shading means positioned between each of saidpairs of pole piece rings to provide alternately shaded and unshadedpole pieces, and a rotor magnetically associated with said magneticfield structure.

14. In an alternating current motor, a magnetic core with an energizingwinding thereon, a magnetic field structure energized by said magneticcore and including pole piece structures attached to either end of saidmagnetic core and being concentric therewith, each of said pole piecestructures including a pair of pole piece rings having pole piecesthereon extending axially of said magnetic core, all of said pole piecesoriginating from said pole piece structures at the same radial regionadjacent one end 0! said magnetic core, a single shading meanspositioned between each of said pairs of pole piece rings to providealternately shaded and unshaded pole pieces, and a rotor magneticallyassociated with said magnetic field structure.

15. In an alternating current motor, a magnetic core with an energizingwinding thereon, a magnetic field structure energized by said magneticcore and including pole piece structures attached to either end 01 saidmagnetic core, and being concentric therewith, each of said pole piecestructures including a pair of pole piece rings having pole piecesthereon extending axially of said magnetic core. all ofsaid pole piecesoriginating from said pole piece structures at the same radial regionadjacent one end of said magnetic core, the pole piece rings of one ofsaid pole piece structures attached to one end 01 said magnetic corebeing spaced radially from the pole piece rings or the other of saidpole piece structures attached to the other end of said magnetic core toprovide an annular air gap therebetween, a single shading meanspositioned between said rings 01 each of said pole piece structures toprovide alternately shaded and unshaded pole pieces, and a rotorpositioned to rotate within said annular air gap.

16. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic held structure housing said magnetic core and saidenergizing winding and being energized from the same, said magneticfield structure including a plurality of inner and outer pole piecerings with pole pieces thereon extending axially of said magnetic core,said inner and outer pole piece rings being located in the same relativeposition with respect to said core and being magnetically connected toopposite extremities of said core, shading means located between saidinner rings and between said outer rings to provide rings of shaded andrings of unshaded pole pieces, means-securing said inner pole piecerings and their shading means to one end of said mag netic core inassembled relationship, means connecting said outer pole piece rings andtheir shading means in assembled relationship including a plurality oftapped bushings, a gear train positioned on said magnetic fieldstructure at said tapped bushings and secured thereto by screws whichthread into said tapped bushings, a rotor of high magnetic retentivityjournaled in said gear train and magnetically associated with saidmagnetic field structure, and a cup-shaped cover member of nonmagneticmaterial enclosing said gear train and said pole pieces of said magneticfield structure.

.17. In asynchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure housing said magnetic core and saidenergizing winding and being energized from the same, said magneticfield structure including a plurality of inner and outer pole piecerings with pole pieces thereon extending axially of said magnetic core,said inner and outer pole piece rings being located to the side of oneextremity of said magnetic core and being magnetically connected toopposite extremities of said magnetic core, shading means locatedbetween said inner rings and between said outer rings to provide ringsof shaded and rings of unshaded pole pieces, means securing said innerpole piece rings and their shading means to one end of said magneticcore in assembled relationship, means connecting said outer pole piecerings and their shading means in assembled relationship including aplurality of tapped bushings, a gear train positioned on said magneticfield structure at said tapped bushings and secured thereto by screwswhich thread into said tapped bushings, and a rotor oi! high magneticretentivity :Iournaled in said gear train and magnetically associatedwith said magnetic field structure, and a cup-shaped cover member ofnonmagnetic material enclosing said gear train and said pole pieces ofsaid magnetic field structure.

18. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure housing said magnetic core and saidenergizing winding and being energized from the same, said magneticfield structure including a plurality of inner and outer pole piece ringwith pole pieces thereon extending axially of said magnetic core, saidinner and outer pole piece rings being located to the side of oneextremity of said magnetic core and being magnetically connected toopposited extremities of said magnetic core, shading means locatedbetween said inner rings and between said outer rings to provide rings01' shaded and rings of unshaded pole pieces, means securing said 17inner pole piece rings and their shading means to one end of saidmagnetic core in assembled relationship, means connecting said outerpole piece rings and their shading means in assembled relationshipincluding a plurality of tapped bushings, a gear train positioned onsaid magnetic field structure at said tapped bushings and securedthereto by screws which thread into said tapped bushings, a rotor ofhigh magnetic retentivity journaled in said gear train and magneticallyassociated with said magnetic field structure, and a cup-shaped covermember of nonmagnetic material enclosing said gear train and said polepieces of said magnetic field structure, said cover member being of thesame diametrical dimensions as said magnetic field structure and beingsecured to said gear train and said magnetic field structure by a liquidtight seal. 19. In a synchronous motor, a magnetic core with anenergizing winding thereon, a magnetic field structure housing saidmagnetic core and said energizing winding and being energized from thesame, said magnetic field structure including a plurality of inner andouter pole piece rings with pole pieces thereon extending axially ofsaid magnetic core, said inner and outer pole piece rings being locatedin the same relative position with respect to said core and beingmagnetically connected to opposite extremities of said core, shadingmeans located between said inner rings and between said outer rings toprovide rings of shaded and rings of unshaded pole pieces, meanssecuring said inner pole piece rings and their shading means to one endof said magnetic core in assembled relationship, means connecting saidouter pole piece rings and their shading means in assembled relationshipincluding a plurality of tapped bushings, a gear train positioned onsaid magnetic field structure at said tapped bushings and securedthereto by screws which thread into said tapped bushings, said geartrain including a pair of side plates which hold the gears in assembledrelationship, said side plates being held together by tapped sleevemembers through which said screws thread to fit into said tappedbushings, one of said tapped sleeve elements having a transverse ducttherethrough, a cup-shaped rotor element of high magnetic materialjournaled on said gear train and magnetically associated with saidmagnetic field structure, and a cup-shaped cover member of nonmagneticmaterial enclosing said gear train and fitting onto said magnetic fieldstructure, one 01' said screws being threaded through said tapped sleeveelement having said transverse duct and into a tapped bushing through anaperture in said casing.

20. In a motor, a magnetic field structure including an energizing corewith a winding thereon and a plurality of pole piece members attached tosaid magnetic core, one of said pole piece members being cup shaped inform and positioned to substantially encircle said core and saidwinding, said one of said pole piece members having a continuousperipheral shoulder thereon, a rotor magnetically associated with saidfield structure, a gear train connected to said rotor and mounted onsaid field structure, casing means having a periphery of the same shapeas said shoulder resting on said shoulder of said pole piece member in atelescopic manner and enclosing said gear train and said rotor, andmeans including said gear train for securing said casing member on saidshoulder of said pole piece member.

21. In a motor, a magnetic field structure in: cluding an energizingcore with a winding thereon and a plurality of pole piece membersattached to said core, one or said pole piece members having acontinuous peripheral shoulder portion thereon, a rotor magneticallyassociated with said field structure, a gear train attached to saidrotor, means including a plurality of sleeve members mounting said geartrain is assembled relationship on said field structure, one of saidsleeve members having a passage therein communicating with a lubricatingmeans for said gear train, a cover having a peripheral shape similar tosaid shoulder portion or said one of said pole piece members resting onsaid shoulder of said pole piece member and enclosing said gear trainand rotor, said cover havingan aperture therein aligned with said sleevemember having said passage therein, and means mounted in one of saidsleeves from without said cover through said aperture.

22. In a motor, a magnetic field structure including an energizing corewith a winding thereon and a plurality of pole piece members attached tosaid core, a rotor magnetically associated with said field structure, agear train attached to said rotor, means including a plurality of sleevemembers mounting said gear train in assembled relationship on said fieldstructure, one of said sleeve members having a passage thereincommunicating with a lubricating means for said gear train, a covermeans mounted on said field structure enclosing said gear train and saidrotor, said cover means having an aperture therein aligned with saidsleeve member having said passage, and means mounted in said one of saidsleeves through said aperture in said cover and from without said coverfor securing said cover to said gear train.

23. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure including inner and outer portionswith pole pieces thereon extendingaxially of said core and beingconcentric therewith, all of said pole pieces originating from saidportions of said structure at the same radial region with respect to oneend of said magnetic core, means connecting respectively said outer andinner portions to opposite extremities of said magnetic core, shadingmeans encircling alternate pole pieces of said inner and outer portionsto provide alternately shaded and unshaded pole pieces thereon, and arotor magnetically associated with said magnetic field structure.

24. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure including inner and outer portionswith pole pieces thereon extending axially of said core and beingconcentric therewith, all of said pole pieces originating from saidportions of said structure at the same radial region with respect to oneend of said magnetic core and with said outer portion being in part anannular shell encircling said core and said winding thereon, meansconnecting respectively said outer and inner portions to oppositeextremities of said magnetic core, shading means encircling alternatepole pieces of said inner and outer portions to provide alternatelyshaded and unshaded pole pieces thereon, and a rotor magneticallyassociated with said magnetic field structure.

25. In a synchronous motor, a magnetic core with an energizing windingthereon, a magnetic field structure including inner and outer portionswith pole pieces thereon extending axially of said core and beingconcentric therewith, all of said pole pieces originating from saidportions of said structure at the same radial region with respect to oneend of said magnetic core and with said outer portion being in part anannular shell encircling said core and said winding thereon, meansmagnetically connecting respectively said inner and outer portions toopposite extremities of said aniagnetic core, said pole pieces of saidouter portion being spaced radially from the pole pieces of said innerportion to provide an annular air gap therebetween, shading meansencircling alternate pole pieces of said inner and outer portions toprovide alternately shaded and unshaded pole piece thereon, and a rotorpositioned to rotate within said annular air gap.

CARL G. KRONMIILER. WILLIS H. GILLE.

20 REFERENCES crrnn The following references are of record in the illeof this patent:

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